The present invention relates to an ignition system with an ignition coil that is supplied at the primary side by a high frequency source (HF source), wherein the voltage provided by the HF source is pulse width modulated and a means for picking up the secondary side current (actual value) is provided.
In EP 0 547 258 A1 the peak value of the current flowing in the spark plug or secondary electrical circuit at the time of ignition or shortly thereafter is compared with a reference value by regulating the closing time. If, for any reasonxe2x80x94transformation ratio or condition of the ignition coil, plug or cable etcxe2x80x94the peak value is greater or less than the pre-determined reference value, the closing time of the primary electric circuit is correspondingly shortened or lengthened.
Modern ignition systems are therefore no longer content with producing an ignition spark, but instead want to configure the development or pattern of the ignition spark for each individual ignition spark in order to obtain optimum combustion. It is already known to use a high frequency source as the primary side supply for an ignition coil and to pulse width modulate the voltage provided by the high frequency.
From documents JP 55060664 A, JP 53090531 A and JP 01008357 A moreover, ignition control means are known wherein the primary side feed signal is controlled dependent upon the secondary side measurement signals. In JP 55060664 A, control takes place on the primary side when the secondary side current is less than a previously defined threshold value. In JP 5309031 A, the secondary side current strength and combustion time is enlisted as a control value. In JP 01008357 A, a pulse width control system is provided to control the primary side switching on the basis of an output signal picked up on the secondary side.
According to the invention, the aim is now to afford an opportunity to configure the development or pattern of the ignition spark in a freely pre-selectable manner.
It is thus provided according to the invention that a regulating means is provided that regulates the pulse width depending on the picked-up actual value of the current on the secondary side of the ignition coil and on a pre-selected reference value development of the current amplitude during an ignition spark. In this way a reference value development or pattern for the ignition current during an ignition spark can be pre-selected. The regulating means picks up the actual value of the current during the ignition spark, and then, by means of the pulse width modulation, influences the current output such as to substantially retain the reference value development in terms of current amplitude.
In addition, or alternatively it can be provided that the voltage regulation is such that the secondary side ignition voltage is limited to a maximum value. With such regulation, it is possible in particular to obtain a voltage limit for the secondary side ignition voltage.
Finally, it should be noted that a variant in the abovementioned embodiments exists wherein the frequency of the high frequency source is matched to the resonance frequency of the ignition circuit.